Refrigerant compressor having linear drive

ABSTRACT

A coolant compressor has a hermetically sealed compressor housing, in the interior of which lies a piston cylinder unit that compresses a coolant. The cylinder housing of the piston cylinder unit is closed at the front end thereof by a cylinder head. A linear drive is provided, comprising at least one oscillating body which is surrounded by an excitation winding and which is connected to the piston to move same along a longitudinal axis in an oscillating manner. The piston cylinder unit has at least one first permanent magnet that lies on the piston, and at least one second permanent magnet that lies on the cylinder housing. Both magnets face each other and are oriented in the same magnetic pole direction in order to generate a repelling effect between both magnets to limit the path of the piston in the region of the top or bottom dead center.

The invention relates to a refrigerant compressor having a hermetically sealed compressor housing, in whose interior a piston-cylinder unit which compresses a refrigerant is arranged, whose cylinder housing is frontally closed by means of a cylinder head, in which a suction opening and a pressure opening are provided, via which refrigerant is suctioned in via a suction valve through the suction opening and compressed via a pressure valve through the pressure opening, the piston-cylinder unit having at least one piston guided in a piston bore of the cylinder housing, a workspace for compressing a refrigerant being formed between the cylinder head and a first front side of the piston, a linear drive being provided, comprising at least one oscillating body enclosed by an exciter coil, which is connected to the piston in order to move it in an oscillating manner along a piston longitudinal axis, according to the preamble of claim 1.

The refrigerating machine process using azeotropic gases has been known per se for some time. The refrigerant is heated and finally superheated by absorbing energy from the space to be cooled in a vaporizer, which results in vaporization, and is compressed to a higher pressure level by means of a piston-cylinder unit of the refrigerant compressor, where it releases heat via a condenser and is conveyed back into the vaporizer again via a throttle, in which pressure reduction and cooling of the refrigerant occur. Such refrigerant compressors are used in the domestic and industrial fields, where they are typically arranged on the back side of a refrigerator or refrigerated shelf.

The piston-cylinder unit comprises a cylinder housing provided with a piston bore, in which an oscillating piston is guided.

The piston bore of the cylinder housing is closed in a first axial end area by a cylinder head or by a valve plate, while the piston bore is open in a second axial end area for accommodating the piston or is penetrated by a connecting rod in the installed state of the refrigerant compressor.

The cylinder head can be implemented in general, on the one hand, as a solid, cap-shaped component, for example, having a pressure chamber and a suction chamber, which carries a valve plate on its inner side. It can be implemented as a ring-shaped component, which holds the valve plate on the cylinder housing, however, it can also be implemented solely as a valve plate, which is clamped by means of a clamping device on the cylindrical part of the cylinder housing. The suction opening for suctioning the refrigerant out of the refrigerant circuit is then arranged in the valve plate, as well as the pressure opening, through which the compressed refrigerant is expelled by the piston after the compression procedure in the refrigerant circuit.

The valve plate is screwed together with the front side of the cylinder housing in the most widespread refrigerant piston compressors. For this purpose, bores are arranged both on the cylinder housing and also in the valve plate, the bores in the cylinder housing each being provided with a thread, via which the screw connection is performed. On the side of the valve plate opposite to the cylinder housing, in this most widespread type of refrigerant compressors, a cylinder cover is provided, which has a pressure chamber, in which compressed refrigerant expelled from the cylinder is briefly buffered in order to overflow into the refrigerant circuit thereafter. Exemplary embodiments are also known in which a suction chamber corresponding to the pressure chamber is provided, via which the refrigerant is suctioned through the suction opening into the cylinder. Pressure chamber and suction chamber are separated from one another by appropriate structural measures in the cylinder cover in such cases.

A refrigerant compressor of conventional construction comprises an electric motor, which drives the piston oscillating in the piston bore via a crankshaft.

To make the provision of a crankshaft superfluous, diverse linear compressor solutions exist, in which the piston is driven directly by an electric linear drive. In this case, the piston is connected to an oscillating body, which, enclosed by an exciter winding (also referred to as a stator) is set into movement in an oscillating manner along a piston longitudinal axis. The piston stroke (=piston travel) can be determined by a variably induced voltage on the linear drive.

The exact delimitation of the piston travel during oscillation of the piston is problematic in such solutions. On the one hand, the piston is to be prevented from striking in the region of the top dead center on the cylinder head or on the valve plate arranged in the cylinder head. On the other hand, however, the top dead center of the piston is also to be prevented from being displaced too far downward, or the piston approaching the cylinder head or the valve plate is to be prevented from executing a reversal movement excessively early, thus resulting in a performance-reducing dead space.

Mechanical spring elements for buffering the piston and therefore for delimiting the piston travel are proposed for this purpose in publications CN 101240793 A and DE 10 2006 009 270 A. Changing the piston travel by means of adjustable spring elements is known from DE 10 2006 009 256 A.

The disadvantage of such systems is mechanical wear in the spring elements and the piston components. The spring elements occupy valuable space and have proven to be inflexible if the refrigerating capacity of the refrigerant compressor or the piston stroke are to be changed.

Linear compressors also exist in which the piston is exclusively held in position during its oscillation by an electronic controller of the linear drive. Such solutions for delimiting the piston travel, which are known, e.g., from WO 01/48379 A and WO 2009/103138 A2, are only implementable with provision of complex sensor and analysis technology, however. In particular, sensors are provided which ascertain the duration of a piston movement, which is compared thereafter by a microprocessor to a reference duration stored on a storage medium and the current position of the piston is calculated therefrom. Such systems are costly and are therefore hardly used in standard compressor manufacturing.

The present invention is therefore based on the problem of proposing a simple and reliable possibility for delimiting the piston travel in refrigerant compressors having linear drive, which makes both provision of mechanical spring elements and also provision of complex sensor and control electronics for delimiting the piston travel superfluous. Dead space occurring in the cylinder housing is to be reduced as much as possible.

These problems are solved according to the invention by a device having the characterizing features of claim 1.

It is provided that the piston-cylinder unit is equipped with at least one permanent magnet arrangement, comprising respectively at least one first permanent magnet arranged on the piston or on a component connected to the piston and at least one second permanent magnet arranged on the cylinder housing or on a component connected to the cylinder housing, the first permanent magnet and the second permanent magnet respectively having the same magnetic pole direction to one another, in order to generate a repelling action between the two permanent magnets to delimit the piston travel in the region of the top dead center and/or in the region of the bottom dead center upon approach of the first permanent magnet to the second permanent magnet.

The piston travel of the piston can be limited simply and reliably in this manner. Striking of the piston on elements of the cylinder housing, in particular on the valve plate, is also prevented without electronic sensor and control elements.

Fundamentally, an arbitrary number of first and second permanent magnets can be arranged in arbitrary position and configuration.

The component connected to the piston, on which the at least one first—movable—permanent magnet is arranged, can be the oscillating body or a piston shaft connecting the piston to the oscillating body in a special embodiment variant of the invention.

The component connected to the cylinder housing, on or in which the at least one second—fixed—permanent magnet is arranged, is the cylinder head in a preferred embodiment variant of the invention.

A valve plate can be arranged in the cylinder head, the at least one second permanent magnet being arranged on the valve plate, preferably being at least sectionally countersunk in the valve plate. In this way, the piston travel is delimited in the region of the top dead center. The second permanent magnet can be arranged both externally and also internally on or even entirely or partially in the valve plate. The delimitation of the piston travel in the bottom dead center can also be performed using permanent magnets, however, it can also be performed conventionally, for example, by means of spring elements.

According to an alternative embodiment variant of the invention, the component connected to the cylinder housing, on or in which the at least one second permanent magnet is arranged, is a housing enclosing the oscillating body. This housing preferably is a support for the exciter winding (the stator) or the exciter winding itself.

According to a particularly preferred embodiment variant of the invention, the at least one second permanent magnet is arranged inside the piston bore of the cylinder housing, in particular inside the working space or delimiting the working space. Thus, for example, one of the permanent magnets could be countersunk into the cylinder housing so that it delimits the working space using its front side. The working space is formed by the cylinder housing and designates the space within the cylinder housing which the piston passes through during its oscillation.

As already mentioned, it would also be possible according to a further embodiment variant of the invention to arrange the second permanent magnet outside the piston bore or the working space.

Of course, the at least one first permanent magnet can also be arranged outside the piston bore or the working space, e.g., as already proposed above, on the oscillating body or on the piston shaft.

There can be provided a different or further permanent magnet arrangement, in order to delimit the piston travel alternatively or additionally in the region of the bottom dead center, the at least one second permanent magnet being arranged in an end region of the cylinder housing, the end region facing the cylinder head. It is sensible if the at least one first permanent magnet is arranged on a second front side of the piston facing away from the cylinder head or on a piston shaft.

A particularly simple embodiment provides that the at least one first permanent magnet is arranged in the region of the first front side of the piston facing toward the cylinder head.

To avoid dead space losses, it can be provided that—as already in the case of the second permanent magnets—the at least one first permanent magnet is sectionally or entirely countersunk in the front side and/or in the piston shaft. In particular, it is possible that the countersunk first and/or second permanent magnet is sheathed, preferably sheathed on all sides, by the material of the piston or the cylinder head or the valve plate.

According to a refinement of the invention, it is provided that the permanent magnet is countersunk into the front side of the piston and/or the valve plate so that at least one free space, which communicates with the working space, is provided between permanent magnet and piston or permanent magnet and valve plate. This free space preferably extends along the entire periphery of the permanent magnet. The gap-shaped recess promotes free unfolding of the magnetic action of the permanent magnet or expansion of the magnetic field lines originating from the permanent magnet.

Expansion of the magnetic field lines originating from the permanent magnet is promoted further in that the free space is implemented as a gap according to a preferred embodiment variant of the invention, whose clear opening width widens in the direction of the working space.

The free space can be filled using a non-ferromagnetic material, such as plastic. Through such filling of the recess, undesired dead space (remaining space between piston and cylinder head or valve plate in the top dead center of the piston), which would decrease the performance of the refrigerant compressor, can be avoided.

According to another preferred embodiment variant of the invention, the first permanent magnet arranged on the piston side is arranged opposite to the second permanent magnet arranged on the cylinder housing. For example, both permanent magnets can be arranged congruently in the piston longitudinal axis.

For optimal pairing of the first permanent magnet arranged on the piston side and the second permanent magnet arranged on the cylinder housing side, measures according to the invention are proposed hereafter. In each case a focused action of the permanent magnets on one another and a stable location of the piston, in particular during its reversal movement at the dead centers, are to be ensured.

The permanent magnets can be implemented as substantially cylindrical.

In particular, the permanent magnets can be implemented as substantially ring-shaped, the ring shape preferably extending rotationally-symmetric to the piston longitudinal axis. The permanent magnets preferably have a ring-cylindrical shape in this case, so that countersunk permanent magnets can be enclosed by a free space in the form of a ring gap.

The permanent magnets can also be arranged rotationally-symmetric to an axis which is parallel to the piston longitudinal axis.

Arbitrary modifications to the ring shape are also possible, e.g., oval or elliptical shapes. Alternative embodiment variants would be, e.g., spiral-shaped or lattice-shaped permanent magnets. In a special embodiment variant, multiple permanent magnets are arranged concentrically around the piston longitudinal axis.

If the front side of the at least one first permanent magnet arranged on the piston side extends substantially parallel to the front side of the at least one second permanent magnet arranged on the cylinder housing side, uniform implementation of the magnetic field is ensured.

According to a further preferred embodiment variant of the invention, the first permanent magnet arranged on the piston side substantially has an equal field strength, therefore, in the case of identical material preferably a substantially equal mass, as the second permanent magnet arranged on the cylinder housing side. A symmetrical magnetic field is thus generated.

A uniform magnetic field is also achieved if multiple permanent magnets are arranged on a circle extending concentrically to the piston longitudinal axis, the angle spacing of adjacent permanent magnets being substantially equal. The piston-side permanent magnets and the cylinder-housing-side permanent magnets are expediently respectively arranged on a circle, piston-side permanent magnets and cylinder-housing-side permanent magnets being diametrically opposite (i.e., being congruent viewed in the piston longitudinal axis).

In a special type of construction, the piston can be implemented as a double piston, comprising two piston sections arranged on opposing end regions of the double piston, each forming one front side of the double piston. A first working space is formed between the first front side of the double piston and a first cylinder head comprising a first valve plate and a second working space is formed between the second front side of the double piston and a second cylinder head comprising a second valve plate. The oscillating body is arranged between the two front sides of the double piston, preferably enclosed by the double piston, an arrangement according to the invention of permanent magnets being provided for each cylinder head-piston section pair.

In a method according to the invention for establishing the piston travel of a linear compressor in a refrigerant compressor according to the preamble of claim 1, it is provided that the piston-cylinder unit is implemented according to one of claims 1 to 20 and in the case of predefined permanent magnets, the drive strength of the linear drive is set so that the piston changes its movement direction in a predefined top dead center and/or bottom dead center without using a mechanical spring element.

It can be provided, e.g., that the piston only changes its movement direction because of a permanent magnet arrangement in each case both at the top dead center and also at the bottom dead center. However, it can also be provided that the piston only changes its movement direction because of a permanent magnet arrangement in one dead center, while a known spring element is used for the change of the movement direction in the other dead center.

With the permanent magnets, the piston forms a nonlinear mass-spring system jointly with the oscillating body and optionally the piston shaft. Different resonance frequencies are therefore possible in this mass-spring system if the full travel of the mass-spring system is not utilized, while in a linear mass-spring system, for example, in the case of exclusive use of spring elements, only one resonance frequency occurs, at which the piston is normally operated.

Therefore, different piston frequencies and therefore different refrigerating capacities are possible according to the invention.

Correspondingly, it can therefore be provided that—to achieve different refrigerating capacities—a specific frequency of the linear drive is additionally predefined.

As an additional safety measure, so that the piston does not strike on the valve plate, it can be provided that the drive strength and/or frequency of the linear drive are set based on measured position data of the piston or magnetic field strengths. For this purpose, for example, Hall sensors as in inductive encoders or current-voltage measurements of the exciter winding can be used.

The invention will be explained in greater detail on the basis of an exemplary embodiment. In the figures:

FIG. 1 shows a schematic view of a linear compressor according to the invention

FIG. 2 shows a longitudinal section through a piston-cylinder unit according to the invention

FIG. 3 shows a piston-cylinder unit according to the invention having a spring element

FIG. 4 shows a piston-cylinder unit according to the invention having permanent magnets on the oscillating body of the linear drive

FIG. 5 shows the embodiment variant according to FIG. 4, the piston being located in its bottom dead center

FIG. 6 shows a detail “B” from FIG. 4

FIG. 7 shows a modification of the embodiment variant according to FIG. 4 with spring element

FIG. 8 shows a schematic view of the magnetic fields developed in the region of the permanent magnets in the form of field lines (piston in bottom dead center)

FIG. 9 shows a view as in FIG. 8 (piston on the path in the direction of top dead center)

FIG. 10 shows a view as in FIG. 8 (piston reaches top dead center)

FIG. 11 shows a force-distance diagram to illustrate the increase of the magnetic force upon approach of the first permanent magnet to the second permanent magnet

FIG. 12 shows a piston-cylinder unit according to the invention having double piston

FIG. 13 shows a schematic view of a linear compressor according to the invention arranged in a compressor housing.

FIG. 1 schematically shows the construction of a linear compressor 23 according to the invention, which is arranged by means of a suspension device 28 within a hermetically sealed compressor housing 29 (shown in FIG. 13) of a small refrigerant compressor. The linear compressor 23 comprises a piston-cylinder unit 21 having at least one piston 3 guided in a piston bore 2 of a cylinder housing 1. The cylinder housing 1 is frontally closed using a cylinder head 4, more specifically using a valve plate 5 held in the cylinder head 4.

The piston 3 is movable in an oscillating manner by a linear drive 6 along a piston longitudinal axis 9. In a known manner, the linear drive 6 comprises an oscillating body 7, which is rigidly connected or articulated with the piston 3, enclosed by an exciter winding (a stator) 8. In the present exemplary embodiment, the oscillating body 7 is connected by means of a piston rod or a piston shaft 22 to the piston 3.

According to the invention, the piston-cylinder unit 21 is equipped with at least one permanent magnet arrangement (namely two here: 11 a and 12 a; 11 b and 12 b), respectively comprising at least one first permanent magnet 11 a, 11 b arranged on the piston 3 or on a component connected to the piston 3—in particular, this could be the oscillating body 7 or the piston shaft 22 in this case—and comprising at least one second permanent magnet 12 a, 12 b arranged on the cylinder housing 1 or on a component connected to the cylinder housing 1. The at least one first permanent magnet 11 a, 11 b and the at least one second permanent magnet 12 a, 12 b respectively point in the same magnetic pole direction to one another, so that upon approach of the at least one first permanent magnet 11 to the at least one second permanent magnet 12, a repelling effect arises between the two permanent magnets 11 and 12 and therefore an action which delimits the piston travel in the region of the top dead center and/or in the region of the bottom dead center of the piston 3.

In the case of FIG. 1, a first permanent magnet 11 a is attached to the front side of the piston 3 and a further first permanent magnet 11 b, namely a ring-shaped permanent magnet, is attached to the opposing side. A second permanent magnet 12 a is attached to the cylinder head 4 or to its valve plate, and a further permanent magnet 12 b is attached to the opposing side of the cylinder housing 1, where the piston shaft 22 passes through the cylinder housing 1. The latter permanent magnet is implemented as ring-shaped. The permanent magnets 11 a and 12 a cooperate and determine on the basis of their field strength the force increase in the direction of the top dead center of the piston 3, while the permanent magnets 11 b and 12 b cooperate and establish on the basis of their field strength the force increase in the direction of the bottom dead center of the piston 3. Depending on load, the points at which the piston 3 actually reverses can vary.

An embodiment similar to that in FIG. 1 is shown in FIG. 2, except that in FIG. 2 a ring-shaped permanent magnet 11 is countersunk in the first front side 3 a of the piston 3 and a ring-shaped second permanent magnet 12 is countersunk corresponding thereto in the valve plate 5 of the piston 4. The surface of the first permanent magnet 11 facing toward the working space 14 is in a plane with the first front side 3 a of the piston 3. The surface of the second permanent magnet 12 facing toward the working space 14 is in a plane with the level inner surface of the valve plate 5.

The valve plate 5 has a suction opening 17, which is closable on the inner side of the valve plate 5 using a suction valve 15. Furthermore, it has a pressure opening 18, which can be closed on the outer side of the valve plate 5 using a pressure valve 16.

During the intake stroke shown here (the piston 3 moves to the right), the refrigerant flows via the suction opening 17 past the open suction valve 15 into a working space 14 formed between the valve plate 5 and a first front side 3 a of the piston 3 facing toward it. During the compression stroke (the piston 3 moves to the left), refrigerant is conveyed back out of the interior of the cylinder housing 1 via the pressure opening 18. The piston shaft 22 is not shown in FIG. 2.

The two permanent magnets 11, 12 have identical dimensions and are manufactured from the same ferromagnetic material, so that they have equal magnetic field strength. They are implemented as ring cylinders, the inner and the outer surfaces therefore have the shape of a cylindrical sheath, the contact surface on the piston 3 has the shape of a circular ring, as does the surface of the permanent magnets 11, 12 facing toward the working space 14.

Both permanent magnets 11, 12 are countersunk in ring-shaped depressions of the piston 3 or the valve plate 5, respectively, so that the surface of the permanent magnet 11, 12 facing toward the working space 14 terminates level with the first front side 3 a of the piston or with the inner side of the valve plate 5, respectively. The permanent magnets 11, 12 each rest on the base of the ring-shaped depression, between the outer surface of the permanent magnets 11, 12, which is implemented as a cylindrical sheath, and the wall of the depression, however, a free space 13 is provided, so that the magnetic field lines—undisturbed by the metallic material of the piston 3 or the valve plate 5—can exit through the outer surface in the form of a cylindrical sheath of the permanent magnets 11, 12. The free space 13 can also, as shown in the case of the piston 3, be filled using a non-ferromagnetic material, for example, using plastic. The dead space is thus decreased, i.e., the space between the piston in the dead center and the valve plate which can be filled with refrigerant.

The piston travel is delimited at the top dead center by the permanent magnets 11, 12 using the embodiment according to FIG. 2. To delimit the piston travel at the bottom dead center, either a further first permanent magnet, like permanent magnet 11 b in FIG. 1, can also be arranged on the second front side 3 b of the piston 3, with a corresponding permanent magnet 12 b on the cylinder housing.

Or, as shown in FIG. 3, a spring element 27 can be provided, which establishes the bottom dead center of the piston 3. The embodiment of the piston-cylinder unit is equivalent to that of FIG. 2. In addition, the exciter winding 8 is also shown in FIG. 3.

In the embodiment variant according to FIGS. 4-6, the first permanent magnets 11 a, 11 b are not arranged on the piston 3, but rather on the cylindrical oscillating body 7 of the linear drive 6. The corresponding second permanent magnets 12 a, 12 b are arranged on the inner side of the housing 24 of the linear drive 6, so that they align in the direction of the piston longitudinal axis 9 with the permanent magnets 11 a, 11 b.

The permanent magnets 11 a, 11 b, 12 a, 12 b are also implemented as ring cylinders here, but are not countersunk in the oscillating body 7 or the housing 24, respectively, but rather are fastened on the circular surfaces of the oscillating body 7 or on opposing inner walls of the housing 24, respectively. The ring cylinders are arranged concentrically to the piston longitudinal axis 9.

When the piston 3 is located in the top dead center, see FIG. 4, the permanent magnets 11 a and 12 a—viewed in the direction of the piston longitudinal axis 9—have the least possible distance from one another because of the force of the linear drive 6 acting on the oscillating body 7. However, the permanent magnets 11 b and 12 b have the greatest possible distance from one another, which essentially corresponds to the piston stroke of the piston 3.

If the piston 3 is located in the bottom dead center, see FIG. 5, the permanent magnets 11 b and 12 b—viewed in the direction of the piston longitudinal axis 9—have the least possible distance from one another because of the force of the linear drive 6 acting on the oscillating body 7.

However, the permanent magnets 11 a and 12 a have the greatest possible distance from one another, which essentially corresponds to the piston stroke of the piston 3.

FIG. 6 shows detail B from FIG. 4 in enlarged form. The permanent magnets 11 a and 12 a are visible of the one permanent magnet arrangement (a), only permanent magnet 11 b is visible of the second permanent magnet arrangement (b). The radial external diameter of the permanent magnets 11 a and 11 b almost corresponds to the radial diameter of the cylindrical oscillating body 7, the diameter of the permanent magnets 11 a, 11 b, 12 a, 12 b is only approximately 1-5% smaller than that of the oscillating body 7.

FIG. 7 shows a modification of the embodiment variant according to FIG. 4, in that the permanent magnet arrangement for establishing the bottom dead center from FIG. 4 is replaced by a spring element 27. The permanent magnets 11 a and 12 a from FIG. 4 are maintained, the permanent magnets 11 b and 12 b are replaced by the spring element 27.

FIG. 8 shows a schematic view of the magnetic fields developed in the region of the permanent magnets 11, 12 of FIGS. 2 and 3 in the form of field lines 25 or 26, respectively, the piston 3 being located in the region of its bottom dead center. Magnetic field lines are closed, they each exit at the so-called “north pole” from the permanent magnets and enter therein at the so-called “south pole”. When the south pole of a permanent magnet approaches the north pole of another permanent magnet, the permanent magnets attract and adhere to one another. If the north pole of one permanent magnet approaches the north pole of another permanent magnet (or the south pole approaches the south pole of another permanent magnet), the two permanent magnets repel, it is not possible or it is only possible using a specific force for the permanent magnets to approach close enough to one another so that their south poles touch. This principle is utilized in this invention. Since the repelling force between the magnetic poles of the same name is inversely proportional to the distance of the magnetic poles, the force for the approach of the piston 3 to the valve plate 5 is not linear to the distance between piston 3 and valve plate 5. This is a substantial difference from a spring element arranged between valve plate 5 and piston 3, in which the force is linearly dependent on the distance between valve plate 5 and piston 3.

Both valve plate 5 and also piston 3 are manufactured in this exemplary embodiment from steel, i.e., they are ferromagnetic themselves, therefore the magnetic field lines 25, 26 can penetrate into the valve plate 5 and the piston 3. The distance between piston 3 and piston bore 2 is shown exaggeratedly large here.

FIG. 9 shows the piston-cylinder arrangement 21 during the progressing compression stroke, the piston is on the path in the direction of top dead center. The first permanent magnet 11 arranged on the first front side 3 a of the piston 3 approaches the fixed second permanent magnet 12 countersunk in the valve plate 5. The magnetic fields of the two permanent magnets 11, 12 influence one another significantly more than in FIG. 8. In the working region 14, the distance between the separate field lines 25, 26 of the permanent magnets decreases, the magnetic field strength becomes greater, the field lines are “tensioned” similarly to a spring.

According to FIG. 10, the piston 3 has reached its top dead center. Striking of the first front side 3 a of the piston 3 on the valve plate 5 is prevented, since the two permanent magnets 11 and 12 each point toward one another with identical magnetic pole direction (with the “north pole”) and therefore repel one another. If the exciter field of the exciter winding 8 was now turned off, the piston 3 would be displaced to the right by the repelling force of the permanent magnets 11, 12.

The piston travel in the region of the bottom dead center can also be delimited in the same fundamental way as the piston travel was delimited according to FIGS. 8-10 in the region of the top dead center.

FIG. 11 shows a force-distance graph to illustrate the increase of the magnetic force during the approach of the first permanent magnet 11 to the second permanent magnet 12. The distance between first permanent magnet 11 and second permanent magnet 12 in centimeters is plotted on the horizontal axis, the magnetic force F in % is plotted on the vertical axis, 100% representing the repelling magnetic force in the top dead center. This force must be applied by the linear drive 6 and the mass inertia of the piston 3 having oscillating body 7 to hold the piston 3 for a short time in the top dead center. In this example, the top dead center is given at a distance of 0.05-0.5 mm between first permanent magnet 11 and second permanent magnet 12. Both the rhomboid measuring points and also the measuring curve interpolated based on the measuring points are shown.

FIG. 12 shows a piston-cylinder unit according to the invention having a double piston. The piston 3 is implemented as a double piston and comprises two piston sections 19, 20, arranged on opposing end regions and each forming one front side 3 a, 3 b of the double piston. A first working space 14 is formed between the first front side 3 a of the double piston and a first cylinder head 4 comprising a first valve plate 5, and a second working space 14′ is formed between the second front side 3 b of the double piston and a second cylinder head 4′ comprising a second valve plate 5′. The oscillating body 7 is arranged between the two front sides 3 a, 3 b of the double piston, preferably enclosed by the double piston 3. One permanent magnet arrangement 11 a, 12 a or 11 b, 12 b according to the invention is provided for each cylinder head-piston section pair 4/19 or 4′/20.

LIST OF REFERENCE NUMERALS

1 cylinder housing

2 piston bore

3 piston

3 a first front side of the piston

3 b second front side of the piston

4 cylinder head

4′ second cylinder head

5 valve plate

5′ second valve plate

6 linear drive

7 oscillating body

8 exciter winding (stator)

9 piston longitudinal axis

11, 11 a, 11 b first permanent magnet

12, 12 a, 12 b second permanent magnet

13 free space

14 working space of the piston 3

14′ second working space of the piston 3

15 suction valve

15′ second suction valve

16 pressure valve

16′ second pressure valve

17 suction opening

17′ second section opening

18 pressure opening

18′ second pressure opening

19 first piston section of the double piston

20 second piston section of the double piston

21 piston-cylinder unit

22 piston shaft

23 linear compressor

24 housing of the linear drive

25 field lines of the first permanent magnet

26 field lines of the second permanent magnet

27 spring element 

1-23. (canceled)
 24. A refrigerant compressor having a hermetically sealed compressor housing, in whose interior a piston-cylinder unit (21), which compresses a refrigerant, is arranged, whose cylinder housing (1) is frontally closed by means of a cylinder head (4), in which a suction opening (17) and a pressure opening (18) are provided, via which refrigerant is suctioned in via a suction valve (15) through the suction opening and compressed via a pressure valve (16) to the pressure opening, the piston-cylinder unit (21) having at least one piston (3) guided in a piston bore (2) of the cylinder housing (1), a working space (14) for compressing a refrigerant being formed between the cylinder head (4) and a first front side (3 a) of the piston (3), a linear drive (6) being provided, comprising at least one oscillating body (7) enclosed by an exciter winding (8), which is connected to the piston (3), in order to move it along a piston longitudinal axis (9) in oscillating manner, the piston-cylinder unit (21) being equipped with at least one permanent magnet arrangement, comprising respectively at least one first permanent magnet (11) arranged on the piston (3) or on a component connected to the piston (3), wherein the at least one permanent magnet arrangement comprises at least one second permanent magnet (12) arranged on the cylinder housing (1) or on a component connected to the cylinder housing (1), the first permanent magnet (11) and the second permanent magnet (12) pointing toward one another with the same magnetic pole direction in each case, to generate a repelling effect between the two permanent magnets (11, 12) to delimit the piston travel in the region of the top dead center and/or in the region of the bottom dead center upon approach of the first permanent magnet (11) to the second permanent magnet (12), the component connected to the cylinder housing (1), on or in which the at least one second permanent magnet (12) is arranged, is the cylinder head (4), a valve plate (5) is arranged in the cylinder head (4) and the at least one second permanent magnet (12) is arranged on the valve plate (5), preferably at least sectionally countersunk in the valve plate (5), in order to delimit the piston travel in the region of the top dead center, the permanent magnets (11, 12) are countersunk into the front side (3 a, 3 b) of the piston (3) and/or the valve plate (5) so that at least one free space (13) is provided between permanent magnet and piston or valve plate, which communicates with the working space (14), and this free space (13) extends along the entire periphery of the permanent magnets (11, 12).
 25. The refrigerant compressor according to claim 24, wherein the component connected to the piston (3), on which the at least one first permanent magnet (11) is arranged, is the oscillating body (7) or a piston shaft (22) connecting the piston (3) to the oscillating body (7).
 26. The refrigerant compressor according to claim 24, wherein the at least one second permanent magnet (12) is arranged inside the piston bore (2) of the cylinder housing (1).
 27. The refrigerant compressor according to claim 24, wherein the at least one second permanent magnet (12) is arranged inside the working space (14) or to delimit the working space (14).
 28. The refrigerant compressor according to claim 24, wherein the at least one first permanent magnet (11) is arranged in the region of the first front side (3 a) of the piston (3) facing toward the cylinder head (4).
 29. The refrigerant compressor according to claim 28, wherein the at least one first permanent magnet (11) is sectionally or entirely countersunk in the front side (3 a) and/or in the piston shaft (22).
 30. The refrigerant compressor according to claim 24, wherein the free space (13) is implemented as a gap, whose clear opening width widens in the direction of the working space (14).
 31. The refrigerant compressor according to claim 29, wherein the free space (13) is filled using a non-ferromagnetic material.
 32. The refrigerant compressor according to claim 24, wherein the at least one first permanent magnet (11) is arranged opposite to the at least one second permanent magnet (12).
 33. The refrigerant compressor according to claim 24, wherein the permanent magnets (11, 12) are implemented as essentially ring-shaped, the ring shape preferably extending rotationally-symmetric to the piston longitudinal axis (9) and/or the free space preferably being implemented as a ring gap.
 34. The refrigerant compressor according to claim 24, wherein one front side (11 a) of the at least one first permanent magnet (11) extends substantially parallel to one front side (12 a) of the at least one second permanent magnet (12).
 35. The refrigerant compressor according to claim 29, wherein the at least one first permanent magnet (11) has an essentially equal field strength, preferably an essentially equal mass, as the at least one second permanent magnet (12).
 36. The refrigerant compressor according to claim 29, wherein multiple permanent magnets (11, 12) are arranged on a circle extending concentrically to the piston longitudinal axis (9), the angle spacing of adjacent permanent magnets (11, 12) being essentially equal.
 37. The refrigerant compressor according to claim 24, wherein the piston (3) is implemented as a double piston, comprising two piston sections (19, 20), arranged on opposing end regions of the double piston (3) and each forming one front side (3 a, 3 b) of the double piston, a first working space (14) being formed between the first front side (3 a) of the double piston (3) and a first cylinder head (4) comprising a first valve plate (5) and a second working space (14′) being formed between the second front side (3 b) of the double piston (3) and a second cylinder head (4′) comprising a second valve plate (5′), and the oscillating body (7) being arranged between the two front side (3 a, 3 b) of the double piston (3), preferably enclosed by the double piston (3), and one permanent magnet arrangement according to one of the preceding claims being provided for each cylinder head-piston section pair (4/19, 4′/20). 